Yogurt makes the most moist cakes.
If baking powder is added to the recipe, yogurt helps to activate that resulting in moist cakes.

Thanks for stopping by Namita. In the table it is clearly stated “use 1/4 cup pureed fruit + 1/2 teaspoon baking powder”. I do not see baking soda in that table, are you referring to a particular recipe?
Hummingbird cake uses eggs as well as a fruit in its batter and replacing eggs in that recipe with a pureed fruit may result in a fruity flavored cake. If using applesauce for this cake then you will have a strong apple-y flavor in your cake. Hope that helps!!